This simple implementation writes log messages to stdout/err and flushes
the buffers immediately after the message has been written.
Also update log messages with the certificate CN to a better readable format
Introduce functions for get_cert_cn and get_cert_valid_until to
encapsulate all cryptographic functions consistently in tools.
This may also be used to guarantee a correct TXT record lookup by setting
dns_verify_all_ns=true, a dns_verify_failtime < dns_verify_waittime and
a high enough value of dns_verify_failtime (like 300 seconds)
- Remove wait times returned by create_challenge
- Remove wait loops from authorities
- Add the wait for valid DNS TXT records in the abstract
DNSChallengeHandler start_challenge function.
- Move challenge verification to start_challenge in general
